From: Yuan Fu<casouri@gmail.com>
Date: Wed, 12 Jul 2023 14:11:14 -0700
Cc: Eli Zaretskii<eliz@gnu.org>,
64420@debbugs.gnu.org
Here’s what I know: In a CJK “context”, “…” is supposed to be one ideograph
wide (like all CJK punctuation), ie, width=2.
However, it’s not as simple as “they used the wrong font”, because both Latin
and CJK use the same Unicode code point for “…”, but expect different glyphs.
In publication, this is solved by manually marking the text with style or font,
so the software uses the desired glyph. Terminals and editors don’t have this
luxury.
BTW it’s not just ellipses, CJK and Latin shares the same code points for
quotes, em dash and middle dot while expecting different glyphs for them.
Since most terminal and editor (especially terminal) quires ASCII/Latin font
before falling back to CJK fonts, I expect most terminal and editor to show the
Latin glyph for “…” (width=1) most of the time.
So practically, it would be correct most of the time if we assume the following
code points have a width of 1, regardless of locale:
– HORIZONTAL ELLIPSIS …
– LEFT/RIGHT DOUBLE QUOTATION MARK “”
– LEFT/RIGHT SINGLE QUOTATION MARK ‘’
– EM DASH —
– MIDDLE DOT ·
But obviously if someone configures their terminal or editor to use CJK font
first, these characters MIGHT have width = 2. I said MIGHT because there are
plenty CJK fonts that uses the 1-width Latin glyph for these characters by
default.
It might be helpful to have a wrapper string-width that considers heuristics
like this, while string-width goes strictly by Unicode and locale.